Moderna tumbled in its Wall Street debut after the biggest IPO in biotech history

Moderna Therapeutics started trading Friday in its initial public offering under the ticker "MRNA."

It raised more than $600 million in the biggest IPO in biotech history, selling shares at $23 each.

Moderna's stock closed 19% down from its IPO price, falling to $18.60.

Moderna is developing medical treatments based on messenger RNA, and the company is still in the early days of human trials for its treatments.

Moderna Therapeutics had a rough start on Wall Street Friday after the biggest initial public offering in biotech history.

The stock closed down 19.% to $18.60 in its trading debut on Friday, after pricing at $23 late on Thursday night.

Moderna sold more than 26 million shares late Thursday, raising $604 million, a biotech record. The company trades under the ticker "MRNA."

Moderna is developing medical treatments based on messenger RNA, and the company is still in the early days of human trials for its treatments, which include cancer treatments as well as a vaccine for cytomegalovirus, or CMV.

It's been a big year for biotech IPOs. In October, the early-stage cancer biotech Allogene became the then-biggest biotech IPO ever. It raised $324 million in an IPO that valued the company at more than $2 billion.

But a number of biotech investors are sticking this one out, fearing that Moderna's valuation is too high, an investor familiar with the company told Business Insider.

If Moderna had a more typical valuation for a biotech company, around the billion-dollar range, hard-core biotech investors would likely be more optimistic, the investor said.

Other companies are also working in the messenger RNA space. One, Translate Bio, went public earlier this year at a much smaller market capitalization; it's worth around $421 million.

Others with similar approaches like CureVac and BioNTech remain privately-held.

Excluding Moderna, there have been 56 biotech IPOs that have raised a total $5.5 billion in 2018, according to Renaissance Capital. It's the highest total since 2014, when there were 71 biotech IPOs that raised a combined $5.2 billion.

Morgan Stanley, Goldman Sachs and J.P. Morgan were the joint lead bookrunners on the deal.